Solvent for treating polystyrene resin and method of treating polystyrene resin with the same

ABSTRACT

A solvent for polystyrene resin treatment which is for use in contracting a polystyrene resin by contact therewith and is excellent in treatment rate, stickiness and sedimentation of the substance being treated, etc.; and a method of treating a polystyrene resin with the solvent. The solvent for polystyrene resin treatment, which is a liquid medium for bringing a polystyrene into a jelly- or gel-state and thereby reducing the volume, comprises an aliphatic hydrocarbon and a solvent in which polystyrene resins are soluble, and is characterized in that the mixing proportion of the aliphatic hydrocarbon is 37.5±2.5 wt % based on the liquid medium.

TECHNICAL FIELD

The present invention relates to a solvent for polystyrene resintreatment that is made to contact a polystyrene resin to reduce thevolume of the polystyrene resin, and a method of treating a polystyreneresin using the solvent.

BACKGROUND ART

Polystyrene foam is bulky due to being expanded and lightweight, andmoreover polystyrene foam has a strong structure and hence gasthereinside cannot be contracted and discharged even upon applying aconsiderable external pressure; there is thus a problem that theefficiency of transporting recovered waste polystyrene foam is poor, andthus the transportation cost and the treatment cost are very high.

Regarding methods of reducing the volume of waste polystyrene foam,solvents for polystyrene foam treatment and polystyrene foam treatmentmethods using such solvents have thus been proposed according to whichwaste polystyrene foam is made to come into contact with a liquid mediumin which polystyrene foam is soluble, thus dissolving and hence reducingthe volume of the waste polystyrene foam (Japanese Patent ApplicationLaid-open No. 2-1748, Japanese Patent Application Laid-open No. 5-59212,Japanese Patent Application Laid-open No. 7-113089, etc.).

In these methods, an organic solvent in which polystyrene foam issoluble, for example an organic solvent such as an aromatic compound ora lower aliphatic ketone such as acetone or methyl ethyl ketone, is usedalone, thus dissolving and hence reducing the volume of the wastepolystyrene foam.

However, with these methods in which an organic solvent in whichpolystyrene foam is soluble is used alone, and the polystyrene foamcontacts this organic solvent and is thus dissolved into a liquid, thecost of separating the polystyrene foam from the solution after thetreatment is high, or the solubility of the polystyrene foam per unit ofthe organic solvent used is low, and hence it has not been possible toput these methods into practical use.

Recently, solvents for polystyrene foam treatment and polystyrene foamtreatment methods using such solvents have been mainly researched anddeveloped, wherein a liquid medium comprising a mixture of a solvent inwhich polystyrene foam is soluble such as an aromatic hydrocarbon and asolvent in which polystyrene foam is not soluble such as an aliphatichydrocarbon is used, thus making the polystyrene foam into a resin in asemi-solid swollen state, i.e. the form of a jelly or a paste, and hencereducing the volume of the polystyrene foam (Japanese Patent ApplicationLaid-open No. 9-40802, Japanese Patent Application Laid-open No.9-157435, etc.).

Through such a constitution, waste polystyrene foam can be treated in ashort time period and with less energy, and moreover collection andrecycle of the polystyrene resin after the treatment is easy, not muchspace is required, and a solvent that is relatively cheap can be used.

That is, with these solvents for polystyrene foam treatment, by mixingtogether a solvent in which polystyrene foam is soluble and a solvent inwhich polystyrene foam is not soluble such as an aliphatic hydrocarbon,polystyrene foam is made to have sustained stable solubility in thesolvent for polystyrene foam treatment, and hence compared with aconventional solvent for treating polystyrene foam, a markedly largeramount of polystyrene foam can be treated per unit amount of thesolvent.

However, although commercialization of a considerable number of solventsfor polystyrene foam treatment having a constitution as above has beenattempted to some extent, at present there are virtually no suchcommercialized solvents available on the general market.

The reason for this is that all of the commercialized solvents have hadshortcomings leading to practical problems.

These shortcomings can be roughly summarized as the following (1) to(5).

(1) The flash point is low and hence safety cannot be guaranteed.

(2) The treatment rate is slow, and hence a large amount of polystyrenefoam cannot be treated in a short time period.

(3) The amount of polystyrene foam treated per unit amount of thesolvent is low, and hence running costs are high.

(4) During the treatment, the treated jelly-like or gel-like polystyreneresin floats in the treatment vessel, and hence charging new polystyrenefoam from above is difficult.

(5) The treated jelly-like polystyrene resin is markedly sticky, andhence the efficiency of work such as transferring this polystyrene resininto another vessel is markedly poor.

All solvents that have been commercialized up to now have had at leastone of the above problems (1) to (5), and hence their usage has beenrestricted in practice, and thus none of the solvents has conquered themarket.

Of the above problems, a particularly fatal problem is (5); in the caseof treating polystyrene foam using a solvent for polystyrene foamtreatment as described above, the treated jelly-like or gel-likepolystyrene resin is markedly sticky, and thus sticks firmly to thewalls and bottom of the treatment vessel, or the floor and so on of theworkplace, and hence great effort is required to remove this polystyreneresin, and thus the work efficiency is markedly poor.

Specifically, to reuse the treatment vessel, the jelly-like or gel-likepolystyrene resin have to be removed from the treatment vessel.Polystyrene resin stuck to the walls and bottom of the treatment vesseland so on must be completely scraped off from the treatment vessel byhand using a spatula or the like, and hence the work efficiency is poor,and thus the labor cost and effort required are great, and hence thereis no economic merit in treating the polystyrene foam.

Moreover, if some of the polystyrene resin is adhered to the floor ofthe workplace or the like, then it is difficult to completely removethis polystyrene resin, and hence the floor will continue to be stickyfor a long time period, and leaving this as is is operationallyundesirable.

Furthermore, there is a problem that in work such as transferring andcasting treated jelly-like or gel-like polystyrene resin from one vesselinto another during transport to a dumping site, reprocessing plant orthe like, the handleability, the work efficiency and so on are markedlypoor.

In this way, at present there are the above problems (1) to (5) with thepolystyrene foam treatment method in which polystyrene foam is treatedinto a jelly or gel state to reduce the volume of the polystyrene foam,and in particular the stickiness of the treated polystyrene resin ((5)above) is a very big problem; there are thus strong demands for thedevelopment of, for example, a method according to which the stickinessis reduced, and hence the polystyrene resin handleability and the workefficiency are improved, and polystyrene resin that has become stuck tothe inside of the treatment vessel, the floor of the workplace or thelike can be easily removed.

Consequently, if no suitable improvement is made with regard to theseproblems, then putting solvents for polystyrene foam treatment havingthe above constitution and polystyrene foam treatment methods using suchsolvents into practical use will be a very difficult undertaking.

DISCLOSURE OF THE INVENTION

In view of the above technical background, the present inventor carriedout assiduous studies into solvents for polystyrene foam treatmentaccording to which the above problems (1) to (5) are resolved, and inparticular the stickiness of the treated polystyrene resin is reduced,and hence the work efficiency and handleability are improved, and thepolystyrene resin can be easily recovered, treated and so on with lessenergy, whereby the present inventor eventually accomplished the presentinvention.

That is, the present invention was attained to suitably resolve theabove problems (1) to (5), and in particular has an object thereof toprovide a method of treating a polystyrene resin according to which thestickiness of the treated jelly-like or gel-like polystyrene resin isreduced, and hence the work efficiency and handleability are improved,and the jelly-like or gel-like polystyrene resin can be easilyrecovered, treated and so on with less energy.

The present inventor carried out assiduous studies in view of theproblems of the prior art described above, and as a result discoveredthat a solvent for polystyrene resin treatment that is a liquid mediumfor putting a polystyrene resin into a jelly or gel state to reduce thevolume of the polystyrene resin, wherein the liquid medium comprisesaliphatic hydrocarbon(s) and polystyrene resin-dissolving solvent(s),and wherein the mixing proportion of the aliphatic hydrocarbon(s) in theliquid medium is 37.5±2.5 wt %, gives an excellent polystyrene resintreatment rate and gives a treated polystyrene resin having littlestickiness, thus accomplishing the present invention.

Specifically, the present invention relates to a solvent for polystyreneresin treatment and a method of treating a polystyrene resin as follows.

1. A solvent for polystyrene resin treatment that is a liquid medium forputting a polystyrene resin into a jelly or gel state to reduce thevolume of the polystyrene resin, the liquid medium comprising analiphatic hydrocarbon and a polystyrene resin-dissolving solvent,wherein the mixing proportion of the aliphatic hydrocarbon in the liquidmedium is 37.5±2.5 wt %.

2. The solvent for polystyrene resin treatment according to item 1,wherein the polystyrene resin-dissolving solvent is at least oneselected from compounds having in the molecular structure thereof atleast one functional group selected from benzene rings, ester groups,ketone groups and ether groups.

3. The solvent for polystyrene resin treatment according to item 1,wherein the polystyrene resin-dissolving solvent comprises at least oneterpenic compound.

4. The solvent for polystyrene resin treatment according to item 1,wherein the polystyrene resin-dissolving solvent comprises at least oneselected from the group consisting of xylene, limonene, 2-octanone,ethylene glycol diethyl ether, alkylbenzenes having 9 carbon atoms andalkylbenzenes having 10 carbon atoms.

5. The solvent for polystyrene resin treatment according to item 1, 2 or4, wherein the polystyrene resin-dissolving solvent comprises at leastone selected from the group consisting of xylene, alkylbenzenes having 9carbon atoms and alkylbenzenes having 10 carbon atoms.

6. The solvent for polystyrene resin treatment according to any of items1 through 5, wherein the aliphatic hydrocarbon contains at least 90 wt %of n-tridecane.

7. The solvent for polystyrene resin treatment according to any of items1 through 6, wherein the mixing proportion of the aliphatic hydrocarbonin the liquid medium is 37.5±2.0 wt %.

8. The solvent for polystyrene resin treatment according to any of items1 through 7, wherein the mixing proportion of the aliphatic hydrocarbonin the liquid medium is 37.5±1.5 wt %.

9. A method of treating a polystyrene resin, comprising puttingpolystyrene foam into a dissolved or gel state to reduce the volume ofthe polystyrene foam using the solvent for polystyrene resin treatmentaccording to any of items 1 through 8.

The solvent for polystyrene resin treatment according to the presentinvention is a liquid medium for putting a polystyrene resin into ajelly or gel state to reduce the volume of the polystyrene resin, theliquid medium comprising aliphatic hydrocarbon(s) and polystyreneresin-dissolving solvent(s), wherein the mixing proportion of thealiphatic hydrocarbon(s) in the liquid medium is 37.5±2.5 wt %.

Here, an account of the reasons that it has not been possible to resolvethe above problems (1) to (5) up to now is as follows.

To resolve problem (1), the flash point can be raised by increasing themixing proportion of the aliphatic hydrocarbon(s) in the solvent forpolystyrene resin treatment, but in inverse proportion to this thetreatment rate becomes slower, and hence problem (2) becomes greater.

On the other hand, if the mixing proportion of the aliphatichydrocarbon(s) in the solvent for polystyrene resin treatment is reducedto increase the treatment rate while ignoring problem (1), i.e. whilesacrificing safety, then this time the treatment amount per unit amountof the solvent will drop, and hence problem (3) will become greater.

Moreover, to resolve problem (4) that the treated jelly-like or gel-likepolystyrene resin floats in the treatment vessel, the first means to beproposed is to increase the mixing proportion of the aliphatichydrocarbon(s) in the solvent for polystyrene resin treatment, thusmaking the specific gravity of the solvent for polystyrene resintreatment lower than the specific gravity of the jelly-like or gel-likepolystyrene resin.

However, if the mixing proportion of the aliphatic hydrocarbon(s) in thesolvent for polystyrene resin treatment is increased, then as describedabove the treatment rate will drop, and hence polystyrene foam chargedin will be put into a jelly or gel state while still containing bubbles,and as a result the apparent specific gravity of the treated polystyreneresin will drop, and hence the treated jelly-like or gel-likepolystyrene resin will still float in the treatment vessel, making itvery difficult to resolve problem (4).

Conversely, if the mixing proportion of the aliphatic hydrocarbon(s) inthe solvent for polystyrene resin treatment is reduced to increase thetreatment rate, then this time the specific gravity of the solvent forpolystyrene resin treatment will increase, and hence again the treatedpolystyrene resin will float in the treatment vessel, making it verydifficult to resolve problem (4).

Furthermore, regarding the problem (5) that the treated jelly-like orgel-like polystyrene resin is markedly sticky, and hence the workefficiency is markedly poor, increasing the mixing proportion of thealiphatic hydrocarbon(s) in the solvent for polystyrene resin treatmentmay be increased so that the surface of the treated polystyrene resinwill be coated with the aliphatic hydrocarbon(s), resulting in theimpaired treatment and more pronounced problem (2). Accordingly, thetreated polystyrene resin hardens, thereby lowering fluidity.Consequently, the problem of it being difficult to transfer the treatedpolystyrene resin from one vessel into another during transport to adumping site, reprocessing plant or the like will again arise.

The above problems (1) to (5) are thus intertwined in an irregular andcomplex fashion, with one or more of the problems arising depending onthe mixing proportion of the aliphatic hydrocarbon(s) in the solvent forpolystyrene resin treatment; until now, no research and development hasbeen carried out to set the mixing proportion while considering allabove problems (1) to (5), and in actual practice there have only beensolvents for polystyrene resin treatment for which only improving thetreatment rate has been considered, and solvents for polystyrene resintreatment for which only increasing the flash point has been considered.

These solvents for polystyrene resin treatment have thus hadshortcomings such as the treatment rate being high but the flash pointbeing low and the treatment amount being low, or the flash point beinghigh and hence safety being good but the treatment rate being slow, andfurthermore these solvents for polystyrene resin treatment have also hadvarious other shortcomings such as the treated polystyrene resinfloating in the treatment vessel, or the handleability of the treatedjelly-like or gel-like polystyrene resin being poor, and hence thesesolvents for polystyrene resin treatment have not gained acceptance onthe general market.

To resolve the above problems (1) to (5), the present inventor thuscarried out the following experiments to verify the changes in theproperties of a solvent for polystyrene resin treatment that occur uponchanging the mixing proportion of the aliphatic hydrocarbon(s) in thesolvent for polystyrene resin treatment.

First, the present inventor prepared liquid media comprising a mixtureof an aliphatic hydrocarbon and a polystyrene resin-dissolving solventas experimental solvents for polystyrene resin treatment, changing themixing proportion of the aliphatic hydrocarbon in 5 wt % intervals, andinvestigated the change in the flash point upon the change in the mixingproportion of the aliphatic hydrocarbon at a temperature of 25° C.

The results were that in the case that the mixing proportion of thealiphatic hydrocarbon was changed from 0 up to 30 wt %, the flash pointof the liquid medium comprising a mixture of the aliphatic hydrocarbonand the polystyrene resin-dissolving solvent was dominated by the flashpoint of the polystyrene resin-dissolving solvent which has a low flashpoint, and hence over this range of the mixing proportion of thealiphatic hydrocarbon the flash point of the liquid medium hardlychanged but rather remained low.

However, it was found that when the mixing proportion of the aliphatichydrocarbon exceeded 30 wt %, the flash point of the liquid mediumincreased gradually, and when the mixing proportion of the aliphatichydrocarbon exceeded 35 wt %, the flash point rose rapidly.

Next, the present inventor carried out similar experiments to the above,thus investigating the change in the treatment rate upon a change in themixing proportion of the aliphatic hydrocarbon.

In these experiments, a polystyrene foam cube (10 g) was taken as a testpiece, and this test piece was put into 100 g of the liquid medium, andthen the time taken for the test piece to be completely treated in theliquid medium was measured, whereby the treatment rate per unit amountof polystyrene foam (g/s) was calculated; a comparison was carried outof this treatment rate.

The results were that in the case that the mixing proportion of thealiphatic hydrocarbon was changed from 0 up to 30 wt %, there was hardlyany change in the treatment rate.

However, it was found that when the mixing proportion of the aliphatichydrocarbon exceeded 35 wt %, the treatment rate gradually becameslower, and when the mixing proportion of the aliphatic hydrocarbonexceeded 40 wt %, the treatment rate became yet slower.

Next, the present inventor carried out similar experiments to the above,thus investigating the change in the treatment amount upon a change inthe mixing proportion of the aliphatic hydrocarbon.

In these experiments, polystyrene foam was put into 100 g of the liquidmedium and the amount of the polystyrene foam that could be treated perunit amount of the liquid medium was measured; a comparison was carriedout of this treatment amount.

The results were that in the case that the mixing proportion of thealiphatic hydrocarbon was changed from 0 up to 30 wt %, there was hardlyany changes in the treatment amount.

However, it was found that when the mixing proportion of the aliphatichydrocarbon exceeded 30 wt % the treatment amount gradually increased,and when the mixing proportion of the aliphatic hydrocarbon exceeded 35wt % the treatment amount increased rapidly, and then when the mixingproportion of the aliphatic hydrocarbon reached 40 wt % the treatmentamount virtually reached a limit.

The above three sets of experiments were carried out using aliphatichydrocarbons having various numbers of carbon atoms and variouspolystyrene resin-dissolving solvents (aromatic hydrocarbons, esters,ketones and ethers) and changing the combinations thereof asappropriate, and the results were judged in an overall fashion.

As a result, it was found that for the solvents for polystyrene resintreatment, regardless of the types of the aliphatic hydrocarbon and thepolystyrene resin-dissolving solvent, mixing proportions of thealiphatic hydrocarbon at which the conflicting properties flash point,treatment rate and treatment amount are all satisfactory exist between35 and 40 wt %.

Moreover, further experiments were carried out, and as a result ofcarrying out investigations in which the mixing proportion of thealiphatic hydrocarbon was changed in 0.5 wt % intervals between 35 and40 wt %, it was found that mixing proportions of the aliphatichydrocarbon at which the conflicting properties flash point, treatmentrate and treatment amount are all satisfactory exist in a very narrowrange centered on 37.5 wt %.

The reason for this is not clear and is currently being investigated,but it is assumed that it may be because the balance between thespecific gravity of the liquid medium and the treatment rate is verygood; it has also been found that when polystyrene resin is put into aliquid medium for which the mixing proportion of the aliphatichydrocarbon has been set to be within a very narrow range centered on37.5 wt %, then when the polystyrene resin is treated, the treatedpolystyrene resin rapidly sediments at the bottom of the treatmentvessel, and hence is no impediment when putting in new polystyreneresin.

Moreover, surprisingly, it was found that from a mixing proportion ofthe aliphatic hydrocarbon of 35 wt %, the stickiness of the treatedpolystyrene resin becomes very low, and moreover the treated polystyreneresin has a suitable degree of fluidity, and can be cleanly removed fromthe treatment vessel without sticking to the walls or bottom of thetreatment vessel, and moreover that if the proportion of the aliphatichydrocarbon exceeds 40 wt %, then the treated jelly-like or gel-likepolystyrene resin becomes hard, and thus the fluidity thereof is lost,and hence a new problem of it becoming difficult to transfer the treatedpolystyrene resin from one vessel into another during transport to adumping site, reprocessing plant or the like again arises.

That is, it was found that in the case that polystyrene resin is putinto a liquid medium for which the mixing proportion of the aliphatichydrocarbon has been set to be within a very narrow range centered on37.5 wt %, the treated polystyrene resin has very low stickiness, andmoreover has a suitable degree of fluidity, does not stick to the wallsor bottom of the treatment vessel, and can be cleanly removed from thetreatment vessel.

The reason for this is again not clear at present and is currently beinginvestigated, but it is assumed that it may be because the balance ofthe fluidity (hardness) of the treated polystyrene resin for thealiphatic hydrocarbon in the liquid medium is very good.

Based on these experimental results, the solvent for polystyrene resintreatment of the present invention is a liquid medium for putting apolystyrene resin into a jelly or gel state to reduce the volume of thepolystyrene resin, the liquid medium comprising an aliphatic hydrocarbonand a polystyrene resin-dissolving solvent, wherein the mixingproportion of the aliphatic hydrocarbon in the liquid medium is 37.5±2.5wt %; if the mixing proportion of the aliphatic hydrocarbon in theliquid medium is outside this range, then at least one of the aboveproblems (1) to (5) will occur.

That is, with the present invention, through the above constitution, theconflicting properties flash point, treatment rate and treatment amountare all satisfactorily improved, and the handleability and usability ata recycling site, and also the work efficiency can be markedly improved,and as a result all of the above problems (1) to (5) can be resolved.

Following is a more detailed description of the present invention.

There are no particular limitations on the polystyrene resin treated inthe present invention, but polystyrene foam is preferable. Polystyreneresins are used in a very wide range of fields, and it is not possibleto mention all of these, but for example polystyrene resins are used intrays (containers) for food and so on, thermal insulating materials,stationery, containers for recording media (cassette tapes, CDs, MDs,MOs, DVDs, etc.), resin parts of various electric appliances, and so on,and these are included in targets for treatment here.

In the present invention, ‘treat a polystyrene resin into a jelly or gelstate’ means making the polystyrene resin contact the liquid medium(solvent), thus removing bubbles contained inside the polystyrene resin,and coagulating the polystyrene resin into a jelly state (paste state)or gel state (a semi-solid state), thus reducing the volume of thepolystyrene resin.

The liquid medium for treating the polystyrene resin into a jelly or gelstate is a solvent for polystyrene resin treatment having as a principalcomponent thereof a liquid medium comprising a mixture of solvent thatis able to dissolve polystyrene resins alone (polystyreneresin-dissolving solvent) and an aliphatic hydrocarbon.

The content of the polystyrene resin-dissolving solvent in the solventfor polystyrene resin treatment of the present invention is 60 to 65 wt%, preferably 60.5 to 64.5 wt %, more preferably 61 to 64 wt %.

There are no particular limitations on the polystyrene resin-dissolvingsolvent, so long as it is a solvent that is able to dissolve polystyreneresins alone, but in general compound having at least one functionalgroup selected from benzene rings, ester groups, ketone groups, ethergroups and soon in the molecular structure thereof is suitable; aspecific example is at least one selected from aromatic compounds suchas alkylbenzenes such as xylene and ethylbenzene, ester compounds suchas ethyl acetate, ethyl butyrate and ethyl laurate, ketones such asmethyl isobutyl ketone and octanone, ether compounds such as diethylether and diisobutyl ether, and so on.

Moreover, as the compound having at least one functional group selectedfrom benzene rings, ester groups, ketone groups, ether groups and so onin the molecular structure thereof, in addition to the above, at leastone selected from diester compounds such as dimethyl adipate and diethyladipate, compounds represented by the general formula R1-(O—R2)_(n)—O—R3 such as ethylene glycol diethyl ether, diethylene glycoldimethyl ether and triethylene glycol dimethyl ether, glycol ether fattyacid alkyl ester compounds represented by the general formula R4-(O—R5)_(n)—O—CO—R6 such as glycol monomethyl ether acetate, and so oncan also be suitably used in the solvent for polystyrene resintreatment, and furthermore these can also be used mixed with at leastone selected from the previously mentioned polystyrene resin-dissolvingsolvents. Here, R1, R3, R4 and R6 may be the same or different, and eachis preferably an alkyl group having 1 to 6 carbon atoms, more preferablyan alkyl group having 1 to 3 carbon atoms, yet more preferably an alkylgroup having 1 or 2 carbon atoms. Moreover, R2 and R5 may be the same ordifferent, and each is preferably an alkyl group having 2 to 5 carbonatoms, more preferably an alkyl group having 2 or 3 carbon atoms, yetmore preferably an alkyl group having 2 carbon atoms. Moreover, nrepresents an integer from 1 to 5, preferably 1 to 3, more preferably 1or 2.

In addition, despite being compounds not having a benzene ring, an estergroup, a ketone group or an ether group in the molecular structurethereof, at least one selected from terpenic compounds such as limonene,pinene and terpinene can also be suitably used in the solvent forpolystyrene resin treatment. These terpenic compounds can also be usedmixed with at least one selected from the previously mentionedpolystyrene resin-dissolving solvents.

A preferable solvent for polystyrene resin treatment is at least onesolvent selected from the group consisting of alkylbenzenes having 7 to16 carbon atoms, limonene, 2-octanone and ethylene glycol diethyl ether.A more preferable solvent for polystyrene resin treatment is at leastone alkylbenzene selected from alkylbenzenes having 7 to 12 carbonatoms, a yet more preferable solvent for polystyrene resin treatment isat least one alkylbenzene selected from alkylbenzenes having 8 to 10carbon atoms, and the most preferable solvent for polystyrene resintreatment is at least one alkylbenzene selected from the groupconsisting of xylene, alkylbenzenes having 9 carbon atoms andalkylbenzenes having 10 carbon atoms.

Moreover, the content of the aliphatic hydrocarbon in the solvent forpolystyrene resin treatment of the present invention is 35 to 40 wt %,preferably 35.5 to 39.5 wt %, more preferably 36 to 39 wt %.

Examples of the aliphatic hydrocarbon are known aliphatic hydrocarbons,with specific examples being straight chain and branched aliphatichydrocarbons having 6 to 18 carbon atoms such as hexanes, heptanes,octanes, nonanes, decanes, undecanes, dodecanes, tridecanes,tetradecanes, pentadecanes, hexadecanes, heptadecanes and octadecanes,unsaturated aliphatic hydrocarbons, and isomers thereof. Each of thealiphatic hydrocarbon(s) is preferably anoctane, nonanes, decanes,undecanes, dodecanes, tridecanes or tetradecanes, more preferablynonanes, decanes, undecanes, dodecanes or tridecanes, yet morepreferably tridecanes.

One of the above solvents may be used, or two or more may be selectedand used mixed together, and moreover a mixed liquid medium can besuitably used so long as it is a liquid at least under conditions of 1atmosphere and 0° C.

Examples of suitable commercially sold ones of such aliphatichydrocarbons are n-paraffin SL (a mixture of C₁₀ paraffin, C₁₁ paraffinand C₁₂ paraffin), n-paraffin L (a mixture of C₁₀ paraffin, C₁₁paraffin, C₁₂ paraffin and C₁₃ paraffin) and n-paraffin M (a mixture ofC₁₂ paraffin, C₁₃ paraffin and C₁₄ paraffin) made by NipponPetrochemicals Co., Ltd., Isosol 300 and Isosol 400 which areisoparaffins made by Nippon Petrochemicals Co., Ltd., and so on.Moreover, examples of suitable commercially sold n-tridecanes aren-paraffin N-13 made by Japan Energy Corporation and so on.

Moreover, examples of suitable commercially sold unsaturated aliphatichydrocarbons are DODECENE, 56N Polymer and HIMAS Polymer, which areolefins made by Nippon Petrochemicals Co., Ltd., and so on.

The solvent for polystyrene resin treatment of the present invention isa liquid medium comprising an aliphatic hydrocarbon as above and apolystyrene resin-dissolving solvent as above, and has as the biggestcharacteristic feature thereof the feature that the mixing proportion ofthe aliphatic hydrocarbon in the liquid medium is set to within a verynarrow range centered on 37.5 wt %.

In general, the mixing proportion of the aliphatic hydrocarbon in theliquid medium is preferably within a range of 2.5 wt % above or below37.5 wt %, i.e. 37.5±2.5 wt %, more preferably 37.5±2.0 wt %, yet morepreferably 37.5±1.5 wt %.

Note that other additives, e.g. organic or inorganic compounds such asdyes and fragrances, may be added to the solvent for polystyrene resintreatment of the present invention.

In a method of treating a polystyrene resin in which a polystyrene resinis put into a jelly or gel state to reduce the volume of the polystyreneresin using a solvent for polystyrene resin treatment of the presentinvention, to attain the above object, a solvent for polystyrene resintreatment as described above is made to contact the polystyrene resin,thus treating the polystyrene resin. There are no particular limitationson the method of making the solvent for polystyrene resin treatmentcontact the polystyrene resin, but examples are methods commonly used inthe field of treating polystyrene resins with solvents such as immersingand spraying.

There are no particular limitations on the treatment conditions whentreating a polystyrene resin using the solvent for polystyrene resintreatment of the present invention so long as the volume of thepolystyrene resin is reduced, and these conditions can be selected asappropriate in accordance with the amount and form of the polystyreneresin to be treated, the proportions of the constituent components ofthe solvent for polystyrene resin treatment of the present invention,and so on. For example, the treatment can be carried out by chargingpolystyrene foam into the solvent for polystyrene resin treatment of thepresent invention at −30 to 60° C., preferably −15 to 40° C., and makingthe solvent for polystyrene resin treatment contact the polystyrene foamthrough a method such as applying pressure to polystyrene foam thatcomes out above the surface of the solvent so as to immerse thepolystyrene foam. The treatment time is approximately 20 to 80 secondsat normal temperature when using the solvent at an excess on a piece ofpolystyrene foam of size 5 cm×5 cm×5 cm (2.5 g). In the case of a lowertemperature, the treatment time will be longer.

BEST MODE FOR CARRYING OUT THE INVENTION

Examples will now be given so as to describe the present invention inmore detail; however, the present invention is not limited to theseexamples.

EXAMPLE 1

As a solvent for polystyrene resin treatment, a liquid medium comprising62.5 wt % of xylene and 37.5 wt % of n-paraffin L made by NipponPetrochemicals Co., Ltd. was stirred to uniformity, thus obtaining asolvent for polystyrene resin treatment of the present invention.

EXAMPLE 2

As a solvent for polystyrene resin treatment, a liquid medium comprising62.5 wt % of limonene and 37.5 wt % of n-paraffin SL made by NipponPetrochemicals Co., Ltd. was stirred to uniformity, thus obtaining asolvent for polystyrene resin treatment of the present invention.

EXAMPLE 3

As a solvent for polystyrene resin treatment, a liquid medium comprising62.5 wt % of 2-octanone and 37.5 wt % of n-paraffin M made by NipponPetrochemicals Co., Ltd. was stirred to uniformity, thus obtaining asolvent for polystyrene resin treatment of the present invention.

EXAMPLE 4

As a solvent for polystyrene resin treatment, a liquid medium comprising62.5 wt % of ethylene glycol diethyl ether and 37.5 wt % of n-paraffin Lmade by Nippon Petrochemicals Co., Ltd. was stirred to uniformity, thusobtaining a solvent for polystyrene resin treatment of the presentinvention.

EXAMPLE 5

As a solvent for polystyrene resin treatment, a liquid medium comprising62.5 wt % of Swasol 1500 made by Maruzen Petrochemical Co., Ltd., whichhas C₁₀ alkylbenzenes as a principal component thereof (at least 80 wt%), and 37.5 wt % of n-paraffin N-13 made by Japan Energy Corporation asn-tridecane was stirred to uniformity, thus obtaining a solvent forpolystyrene resin treatment of the present invention.

COMPARATIVE EXAMPLE 1a

A liquid medium obtained by stirring to uniformity a mixture of 55 wt %of xylene and 45 wt % of n-paraffin L made by Nippon Petrochemicals Co.,Ltd. was used.

COMPARATIVE EXAMPLE 1b

A liquid medium obtained by stirring to uniformity a mixture of 70 wt %of xylene and −30 wt % of n-paraffin L made by Nippon PetrochemicalsCo., Ltd. was used.

COMPARATIVE EXAMPLE 2a

A liquid medium obtained by stirring to uniformity a mixture of 55 wt %of limonene and 45 wt % of n-paraffin SL made by Nippon PetrochemicalsCo., Ltd. was used.

COMPARATIVE EXAMPLE 2b

A liquid medium obtained by stirring to uniformity a mixture of 70 wt %of limonene and 30 wt % of n-paraffin SL made by Nippon PetrochemicalsCo., Ltd. was used.

COMPARATIVE EXAMPLE 3a

A liquid medium obtained by stirring to uniformity a mixture of 55 wt %of 2-octanone and 45 wt % of n-paraffin M made by Nippon PetrochemicalsCo., Ltd. was used.

COMPARATIVE EXAMPLE 3b

A liquid medium obtained by stirring to uniformity a mixture of 70 wt %of 2-octanone and 30 wt % of n-paraffin M made by Nippon PetrochemicalsCo., Ltd. was used.

COMPARATIVE EXAMPLE 4a

A liquid medium obtained by stirring to uniformity a mixture of 55 wt %of ethylene glycol diethyl ether and 45 wt % of n-paraffin L made byNippon Petrochemicals Co., Ltd. was used.

COMPARATIVE EXAMPLE 4b

A liquid medium obtained by stirring to uniformity a mixture of 70 wt %of ethylene glycol diethyl ether and 30 wt % of n-paraffin L made byNippon Petrochemicals Co., Ltd. was used.

TEST EXAMPLE 1

100 g of each of the solvents for polystyrene resin treatment ofExamples 1 to 5 and the liquid media of Comparative Examples 1 to 4 wasput into a vessel. Four 5 cm×5 cm×5 cm cubes of polystyrene foam (2.5 g)having a foaming magnification of 60× were prepared, and were charged inorder into each of the vessels into which one of the solvents forpolystyrene resin treatment or liquid media had been put, andcomparative tests were carried out into the treatment rate, the amountof polystyrene foam treated, the sedimentation condition of thepolystyrene resin after the treatment, and the stickiness (stickingresistance) of the polystyrene resin after the treatment.

The stickiness tests in the comparative tests were carried out byturning the vessel (two types were used, namely glass and stainlesssteel) upside down for each sample after the charging in of thepolystyrene foam had been completed, and observing the state of stickingof the treated polystyrene resin to the vessel.

The results are shown in Table 1. TABLE 1 Amount of polystyreneTreatment foam Sedimentation Sticking rate treated condition resistanceExample 1 A A A A Comparative B A C B Example 1a Comparative A B B CExample 1b Example 2 B B B A Comparative C B D B Example 2a ComparativeB C C D Example 2b Example 3 B B A A Comparative C B D B Example 3aComparative B C C D Example 3b Example 4 A A A A Comparative B A C BExample 4a Comparative A B B C Example 4b Example 5 A A A AA: Very GoodB: GoodC: PoorD: Very poor

The results were that it was found that the solvents for polystyreneresin treatment of the Examples are superior in terms of all oftreatment rate, treatment amount, sedimentation and sticking resistancecompared with the Comparative Examples for which the mixing proportionof the aliphatic hydrocarbon was changed by plus or minus only 5 wt % upor down from the range of the present invention (35 to 40 wt %).

In particular, with the solvents for polystyrene resin treatment of theExamples, it was observed that with either a glass vessel (beaker) or astainless steel vessel, as soon as turning the vessel upside down, thetreated polystyrene resin immediately falls and separates completelyfrom the vessel, and hence it was found that the stickiness of thetreated polystyrene foam is reduced by a solvent for polystyrene resintreatment having the mixing proportion of the aliphatic hydrocarbon isset according to the present invention.

TEST EXAMPLE 2 Volume Reduction Time and Sedimentation Condition

200 g of the solvent for polystyrene resin treatment obtained in Example5 was put into a glass vessel, a 2.5 g (5 cm×5 cm×5 cm) piece ofpolystyrene foam having a foaming magnification of 60× was chargedtherein, and the time required for volume reduction and the externalappearance of the treated material were observed. Note that the airtemperature was 30.5° C. and the liquid temperature was 30.2° C.

The result was that the volume reduction was completed in 1 minute 32seconds, and the treated material became gel-like and sedimented in thesolvent.

TEST EXAMPLE 3 Volume Reduction Time and External Appearance

200 g of the solvent for polystyrene resin treatment obtained in Example5 was put into a glass vessel, 42 of a polystyrene foam cube 5 cm on aside as used in Test Example 2 were charged therein, and the timerequired for volume reduction and the external appearance of the treatedmaterial were observed. Note that the air temperature was 30.5° C. andthe liquid temperature was 30.2° C.

The result was that the volume reduction was completed in 7 minutes 55seconds, and the treated material became gel-like and sedimented in thesolvent.

TEST EXAMPLE 4 External Appearance and Sticking Resistance

200 g of the solvent for polystyrene resin treatment obtained in Example5 was put into a glass vessel, 42 of a polystyrene foam cube 5 cm on aside as used in Test Example 2 were charged therein, and the externalappearance of the treated material and the stickiness to the vessel wereobserved. Note that the air temperature was 30.5° C. and the liquidtemperature was 30.2° C.

The result was that the treated material became gel-like and it was ableto be easily removed from the vessel very easily.

TEST EXAMPLE 5 Treatment Amount

200 g of the solvent for polystyrene resin treatment obtained in Example5 was put into a glass vessel, one 100 of a polystyrene foam cube 5 cmon a side as used in Test Example 2 were charged therein, the floatingpolystyrene foam pieces on the surface of the solvent was presseddownward, and the volume of polystyrene foam reduced by the solvent wasmeasured.

The result was that 1 g of polystyrene foam could be subjected to volumereduction per 1 cc (0.8 g) of the solvent.

Industrial Applicability

The present invention relates to a liquid medium for putting apolystyrene resin into a jelly or gel state to reduce the volume of thepolystyrene resin, the liquid medium comprising an aliphatic hydrocarbonand a polystyrene resin-dissolving solvent. Moreover, the mixingproportion of the aliphatic hydrocarbon in the liquid medium is strictlycontrolled to be in a very narrow range of 37.5±2.5 wt %, wherebyeffects such as the following are produced: basic properties such as theflash point, the treatment rate and the treatment amount, and safety andso on are improved, and in particular stickiness of the treatedpolystyrene resin is eliminated, and hence the work efficiency and thehandleability can be markedly improved.

More specifically, the present invention enables the following problems(1) to (5) of conventional solvents for polystyrene resin treatment tobe resolved.

(1) The flash point is low and hence safety cannot be guaranteed.

(2) The treatment rate is slow, and hence a large amount of polystyrenefoam cannot be treated in a short time period.

(3) The amount of polystyrene foam treated per unit amount of thesolvent is low, and hence running costs are high.

(4) During the treatment, treated polystyrene resin floats in thetreatment vessel, and hence charging in new polystyrene foam from aboveis difficult.

(5) The treated polystyrene resin is markedly sticky, and hence the workefficiency is markedly poor.

That is, the present invention has been accomplished to resolve theabove problems (1) to (5), and relates to a solvent for polystyreneresin treatment and a method of treating a polystyrene resin using thesolvent according to which in particular the stickiness of the treatedpolystyrene resin is reduced, and hence the work efficiency andhandleability are improved, and thus polystyrene resin can be easilycollected, treated and so on with less energy; the usefulness of thepresent invention is thus very great.

1: A solvent for polystyrene resin treatment that is a liquid medium forputting a polystyrene resin into a jelly or gel state to reduce thevolume of the polystyrene resin, the liquid medium comprising analiphatic hydrocarbon and a polystyrene resin-dissolving solvent,wherein the mixing proportion of the aliphatic hydrocarbon in the liquidmedium is 37.5±2.5 wt %. 2: The solvent for polystyrene resin treatmentaccording to claim 1, wherein the polystyrene resin-dissolving solventis at least one selected from compounds having in the molecularstructure thereof at least one functional group selected from benzenerings, ester groups, ketone groups and ether groups. 3: The solvent forpolystyrene resin treatment according to claim 1, wherein thepolystyrene resin-dissolving solvent comprises at least one terpeniccompound. 4: The solvent for polystyrene resin treatment according toclaim 1, wherein the polystyrene resin-dissolving solvent comprises atleast one selected from the group consisting of alkylbenzenes having 7to 16 carbon atoms, limonene, 2-octanone and ethylene glycol diethylether. 5: The solvent for polystyrene resin treatment according to claim1, wherein the polystyrene resin-dissolving solvent comprises at leastone alkylbenzene selected from alkylbenzenes having 7 to 12 carbonatoms. 6: The solvent for polystyrene resin treatment according to claim1, wherein the polystyrene resin-dissolving solvent comprises at leastone alkylbenzene selected from alkylbenzenes having 8 to 10 carbonatoms. 7: The solvent for polystyrene resin treatment according to claim1, wherein the polystyrene resin-dissolving solvent contains at leastone alkylbenzene selected from the group consisting of xylene,alkylbenzenes having 9 carbon atoms and alkylbenzenes having 10 carbonatoms. 8: The solvent for polystyrene resin treatment according to claim1, wherein the aliphatic hydrocarbon comprises at least 90 wt % ofn-tridecane. 9: The solvent for polystyrene resin treatment according toclaim 1, wherein the mixing proportion of the aliphatic hydrocarbon inthe liquid medium is 37.5±2.0 wt %. 10: The solvent for polystyreneresin treatment according to claim 1, wherein the mixing proportion ofthe aliphatic hydrocarbon in the liquid medium is 37.5±1.5 wt %. 11: Amethod of treating a polystyrene resin, comprising putting polystyrenefoam into a dissolved or gel state to reduce the volume of thepolystyrene foam using the solvent for polystyrene resin treatmentaccording of claim
 1. 12: The solvent for polystyrene resin treatmentaccording to claim 2, wherein the polystyrene resin-dissolving solventcomprises at least one alkylbenzene selected from alkylbenzenes having 7to 12 carbon atoms. 13: The solvent for polystyrene resin treatmentaccording to claim 4, wherein the polystyrene resin-dissolving solventcomprises at least one alkylbenzene selected from alkylbenzenes having 7to 12 carbon atoms. 14: The solvent for polystyrene resin treatmentaccording to claim 2, wherein the polystyrene resin-dissolving solventcomprises at least one alkylbenzene selected from alkylbenzenes having 8to 10 carbon atoms. 15: The solvent for polystyrene resin treatmentaccording to claim 4, wherein the polystyrene resin-dissolving solventcomprises at least one alkylbenzene selected from alkylbenzenes having 8to 10 carbon atoms. 16: The solvent for polystyrene resin treatmentaccording to claim 2, wherein the polystyrene resin-dissolving solventcontains at least one alkylbenzene selected from the group consisting ofxylene, alkylbenzenes having 9 carbon atoms and alkylbenzenes having 10carbon atoms. 17: The solvent for polystyrene resin treatment accordingto claim 4, wherein the polystyrene resin-dissolving solvent contains atleast one alkylbenzene selected from the group consisting of xylene,alkylbenzenes having 9 carbon atoms and alkylbenzenes having 10 carbonatoms. 18: The solvent for polystyrene resin treatment according toclaim 2, wherein the aliphatic hydrocarbon comprises at least 90 wt % ofn-tridecane. 19: The solvent for polystyrene resin treatment accordingto claim 3, wherein the aliphatic hydrocarbon comprises at least 90 wt %of n-tridecane. 20: The solvent for polystyrene resin treatmentaccording to claim 4, wherein the aliphatic hydrocarbon comprises atleast 90 wt % of n-tridecane. 21: The solvent for polystyrene resintreatment according to claim 2, wherein the mixing proportion of thealiphatic hydrocarbon in the liquid medium is 37.5±2.0 wt %. 22: Thesolvent for polystyrene resin treatment according to claim 3, whereinthe mixing proportion of the aliphatic hydrocarbon in the liquid mediumis 37.5±2.0 wt %. 23: The solvent for polystyrene resin treatmentaccording to claim 4, wherein the mixing proportion of the aliphatichydrocarbon in the liquid medium is 37.5±2.0 wt %. 24: The solvent forpolystyrene resin treatment according to claim 2, wherein the mixingproportion of the aliphatic hydrocarbon in the liquid medium is 37.5±1.5wt %. 25: The solvent for polystyrene resin treatment according to claim3, wherein the mixing proportion of the aliphatic hydrocarbon in theliquid medium is 37.5±1.5 wt %. 26: The solvent for polystyrene resintreatment according to claim 4, wherein the mixing proportion of thealiphatic hydrocarbon in the liquid medium is 37.5±1.5 wt %. 27: Amethod of treating a polystyrene resin, comprising putting polystyrenefoam into a dissolved or gel state to reduce the volume of thepolystyrene foam using the solvent for polystyrene resin treatmentaccording to claim
 2. 28: A method of treating a polystyrene resin,comprising putting polystyrene foam into a dissolved or gel state toreduce the volume of the polystyrene foam using the solvent forpolystyrene resin treatment according to claim
 3. 29: A method oftreating a polystyrene resin, comprising putting polystyrene foam into adissolved or gel state to reduce the volume of the polystyrene foamusing the solvent for polystyrene resin treatment according to claim 4.